Abstract
Quantitative Precipitation Estimates from space-based observations
represent an important dataset for understanding the Earth’s
atmospheric, hydrological and energy cycles. Precipitation retrieval
algorithms have been developed and refined over the last few decades and
their accuracy and reliability are becoming increasingly more important
for Earth’s energy budget and human activities. In particular, snowfall
represents a key component of water cycle and contributes significantly
to the Earth’s radiative balance. Accurately quantifying global surface
snowfall is especially important since snow comprises a large percentage
of the annual surface precipitation in many regions. The complexity of
snowflakes particles and the nonlinear relationships between
observations and retrieved variables have moved scientists to
continually develop and enhance retrieval techniques. The present work
aims to improve snowfall retrievals from Passive Microwave (PMW)
sensors. Within the Global Precipitation Measurement (GPM) mission, the
Goddard PROFiling (GPROF) algorithm snowfall retrieval has been chosen
as an example of PMW precipitation product. Since previous works have
demonstrated that GPROF performance strongly depends on the snowfall
type, we developed a Machine Learning technique to classify snowing
regime. A combined CloudSat-GPM dataset has been used to build the
training dataset in which the GPM Microwave Imager (GMI) brightness
temperatures (TB) are associated with a snowfall type, classifying the
snowfall into three classes (‘shallow convective’, ‘deep stratiform’,
‘other’). The snowfall classification was adopted from a CloudSat
classifying technique, based on snowing profiles and cloud
classification. The problem is posed as a supervised learning problem,
using a fully connected deep learning architecture with TB textures
serving as input features. After building, optimizing and applying the
classification method to existing GMI data, an evaluation exercise was
undertaken to assess the classification performance. Results show that
using only 20,000 GMI-CloudSat collocated snowing scenes the accuracy in
retrieving the three classes has exceeded 80%. Being able to classify
snowfall mode will help develop a specific setup for GPROF to improve
detection and retrieval performance.